The present invention relates to a vacuum brake booster for a motor vehicle brake system comprising a rod-like force input member, which is coupled or can be coupled with a brake pedal, a control valve, which can be actuated by means of the force input member, a chamber arrangement having a vacuum chamber, which is connectable to a vacuum source, as well as a working chamber, which is, in accordance with the actuation of the force input member, selectively connectable to the vacuum chamber and to the surrounding atmosphere, wherein the control valve has a control piston actuatable by means of the force input member, which control piston forms together with a valve element a sealing seat having a sealing seat diameter between the working chamber and the surrounding atmosphere, wherein in the region close to the sealing seat a guiding channel is provided through which, upon the opening of the sealing seat, air flows from the surrounding atmosphere into the working chamber due to a pressure difference.
In the course of technical development in the field of automotive engineering, it is becoming possible to reduce the noise level in the passenger compartment of a motor vehicle further and further. But this can also be achieved, in particular, by reducing the emission of such noises through better acoustic insulation of the passenger compartment. However, other noises produced in the vehicle, which were previously masked by the drive noises and rolling noises, are thereby more easily heard. These include, for example, the intake noise of a vacuum brake booster, which occurs when the brake booster is actuated from its rest position. Owing to the actuation, the working chamber, which is evacuated in the initial state, is connected to the surrounding atmosphere, whereupon surrounding air flows into the working chamber in some cases at high velocity in order to provide a servo assistance for the brake actuation, in a manner known per se. The relatively high flow velocities may also give rise to flow noises in frequency ranges lying in the range of human hearing. Experience has shown here that particularly noises which arise in the frequency range between 2.4 kHz and 8 kHz are felt to be disturbing.
In the prior art, various solutions are known for reducing inflow noises in vacuum brake boosters.
For instance, the generic prior art according to document DE 32 43 093 A1 discloses a vacuum brake booster in which a foam element is provided in the control valve, the geometry of which element is configured such that the cross-sectional area of the guiding channel is reduced. This prior art provides, for example, a plurality of cylindrical openings in the foam element which extend parallel to the force input member.
A comparable solution with a foam element is known from the document DE 29 18 734 A1.
Finally, the document DE 39 24 672 A1 discloses a vacuum brake booster in which a nozzle arrangement with relatively complicated geometry, intended to impart a laminar flow to the sucked-in air, is arranged in the control valve.
All the solutions from the prior art provide additional parts with relatively complicated geometry which increase the production costs of such brake boosters undesirably. Moreover, durability problems may arise when using foam parts.